Why Your Furnace Has a Strange Smell

As the weather turns cold and you transition from cooling to heating your home, you might be worried about strange furnace smells floating in the air. Find out what the most common furnace smells could mean and how proactive you should be about them.

The Furnace Smells Musty

Musty furnace smells generally indicate mold growth hiding in the HVAC system. To avoid subjecting your family to these microorganisms, handle this problem right away.

A damp air filter can lead to mold, so wiping out the smell might be as simple as replacing the filter. If that fails to remove the smell, the AC evaporator coil fastened near the furnace may be the culprit. This component collects condensation, which will sometimes trigger mold growth. You’ll need a professional’s help to inspect and clean the evaporator coil. When the problem still won't go away, start thinking about investing in air duct cleaning. This service eliminates hidden mold, no matter where it’s growing in your ductwork.

The Furnace Smells Like Rotting Eggs

This is one of the most worrisome furnace smells because it probably indicates a gas leak. The utility company includes a useful substance called mercaptan to the natural gas supply to make leaks easier to detect.

If you detect a rotten egg smell near your furnace or coming from your ductwork, shut down the heater straightaway. If you remember where the main gas supply valve is, shut that off as well. Then, get out of the house and contact 911, in addition to your gas company. Don’t reenter the house until a professional tells you it’s safe.

The Furnace Has a Sour Stench

If you discover a sour smell that stings your nose while standing near the furnace, this could mean the heat exchanger has cracked. This vital component houses combustion fumes, including carbon monoxide, so cracks could pump unsafe levels of CO gas into your home.

Carbon monoxide poisoning has the potential to be lethal, so shut off your furnace immediately if you notice a sour odor. Then, reach out to an HVAC professional for an inspection. Consider replacing your furnace if a cracked heat exchanger is responsible. For your continued safety going forward, ensure you have working CO detectors on every floor of your home.

The Furnace Smells Dusty

When you start the furnace for the first time each fall, you should expect a dusty odor to show up for a few minutes. This is the smell of six months’ worth of dust burning away as the furnace wakes from its summer slumber. As long as the smell goes away within one day, you don't have anything to worry about.

The Furnace Has a Smoky Smell

Natural gas, oil and propane furnaces are combustion appliances, so they vent fumes to the exterior. A smoky smell can mean the flue is backed up, and now fumes are settling back into your home. The odor can reach through the entire house, endangering your family’s health if you ignore it. So turn off the furnace and get in touch with a professional right away to schedule a repair.

The Furnace Smells Like It's Burning Plastic

Overheating and melting electrical components are the most likely reason for a burning plastic smell to come from your furnace. A failing fan motor is another possibility. If you don’t address the problem, an electrical fire may start, or your furnace could end up with irreparable damage. Turn off the heating system immediately and contact an HVAC technician for help troubleshooting and repairing this unusual furnace smell.

The Furnace Has an Oily Smell

If you have an oil furnace, you might detect this stench whenever the oil filter becomes blocked up. Try replacing it to determine if that resolves the problem. If the smell remains for more than 24 hours after carrying out this step, it may suggest an oil leak. You’ll need help from an HVAC specialist to handle this problem.

The Furnace Reeks of Sewer Odors

Sewer gas smells pretty similar to rotten eggs, so first determine the potential for a natural gas leak. If that’s not the issue, your home's sewer lines could have an issue, such as a dry trap or sewer leak. Try pouring water down the drains, including the basement floor drain, to fill dried-up sewer traps. If the smell lingers, you’ll need to contact a sewer line repair company.

Contact McElroy Service Experts for Furnace Repair

If you're still uncertain, contact an HVAC technician to assess and repair your furnace. At McElroy Service Experts, we offer thorough diagnostic services to determine the problem before repairs begin. Then, we encourage the most viable, cost-effective repairs, along with an up-front estimate for all options. Our ACE-certified technicians can handle just about any heating malfunction, and we back our work with a 100% satisfaction guarantee for one year. For details about why your furnace smells bad or to request furnace repair near you, please contact your local McElroy Service Experts office today.

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